1. Field of the Invention
The present invention relates to a wet type multi-plate friction engaging apparatus, and more particularly, it relates to a wet type multi-plate friction engaging apparatus mainly used as a brake of a transmission, in which friction materials are adhered to only outer tooth plates or outer tooth plates and a flange.
2. Related Background Art
FIG. 2 is an axial sectional view of a conventional wet type multi-plate friction engaging apparatus 70. A drum 61 is secured to a transmission case (not shown), a retainer 59 is disposed on an inner periphery of the drum 61, and outer tooth plates 51 are incorporated in the retainer. Further, inner tooth plates 54 are attached to an outer peripheral surface of a hub 55 rotated in a direction shown by the arrow A and are interposed between the respective outer tooth plates 51. The outer tooth plates 51 and the inner tooth plates 54 are rotated relative to each other. A piston 52 is mounted near a closed end of the drum 61 and is operated by oil pressure supplied to an oil chamber defined between the piston and the side wall of the drum 61. A flange 64 is secured to an open end portion of the drum 61 by a snap ring 63. For friction engagement, the piston 52 is axially shifted to the right in FIG. 2 to urge the outer tooth plates 51.
In order to lubricate the frictional engagement surfaces between the outer tooth plates and the inner tooth plates from an axially central side, the hub 55 is provided with lubricating oil through holes 56 extending radially.
In this conventional wet type multi-plate friction engaging apparatus 70, friction materials 53 are usually secured to the inner tooth plates 54. Further, in another conventional case, friction materials are secured alternately to one side of the outer tooth plates and one side of the inner tooth plates or friction materials are secured to both the outer tooth plates and the inner tooth plates at different radial positions.
However, in the conventional wet type multi-plate friction engaging apparatuses, since the inner tooth plates are rotated at a high speed, lubricating oil included in the friction materials is removed due to high speed rotation, so that the friction materials cannot hold an adequate amount of oil. As a result, during the friction engagement, heat is apt to be generated, thereby causing thermal deformation called heat spot.
Further, in some wet type multi-plate friction engaging apparatuses used in motor bikes, although friction materials are secured to outer tooth plates, since lubricating oil is supplied in an oil bath manner, there arose a problem that squeezing torque in an idling condition is increased.